The present invention relates to semiconductor laser devices, for example, to an optical-disk use semiconductor laser device suitable for data write to optical disks and data read from optical disks.
Conventionally, semiconductor laser devices of the end face emission type have been used as optical-disk use semiconductor laser devices. Optical-disk use semiconductor laser devices necessitate laser light that allows a good spot shape on the optical disk to be obtained, i.e., laser light that allows a good far field pattern to be obtained.
In some cases, there may occur defectives in the far field pattern, particularly ripples in the radiation light, unsuitable as optical disk use. The ripples could be attributed to the cause that guided light is partly scattered from a waveguide so that the guided light and the scattered light are superimposed on each other. Such a phenomenon more likely appears especially when the waveguide width WO is narrowed in order that kinks will not occur even if the semiconductor laser device is enhanced in output power.
This mechanism is explained with reference to FIG. 14, which is a schematic explanatory view as a waveguide 501 is viewed from above. Guided light 503 and scattered light 505, emitted with a distance Ls therebetween, phase difference between an electric field g (θ) of the guided light 503 and an electric field s (θ) of the scattered light varies in a period of 2π(Ls·sin θ)/λ. As a result of this, an angle θ at which phases strengthen each other and an angle θ at which phases weaken each other appear periodically. As an example, fine ripples are superimposed on horizontal radiation light as shown by a characteristic C1 depicted in solid line in FIG. 4. It is noted that a characteristic C2 shown by broken line in FIG. 4 indicates a horizontal radiation distribution without ripples.